Fix incorrect sizeof() arguments in allocations

In a number of places we have

struct X *val;
val = malloc(sizeof(struct Y));

If sizeof(struct Y) < sizeof(struct X) this is obviously dangerous,
but it is incorrect regardless of the relative sizes of the
structures. Fix all of the occurences of this that clang points out
to us.

Caught by clang-analyzer

Change-Id: Iad32b4ae460d3f40a45cf33624973bf52fd167d4
Reviewed-on: http://gerrit.openafs.org/9156
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>